After the president's death, Taft successfully led the conservative coalition's efforts to curb the power of labor unions. Taft was a leading advocate of non-interventionism in foreign policy. He failed in his quests to win the Republican Party's presidential nomination in 1940, 1948, and 1952. Throughout that period he battled New York Governor Thomas E. Dewey (leader of the moderate "Eastern Establishment") for control of the party. Taft's biographer, James T. Patterson, portrayed Taft as honest, conscientious, courageous, dignified, and highly intelligent but also faulted Taft's competitiveness, lack of public-relations skills, and extreme partisanship.[1] A 1957 Senate committee named Taft as one of America's five greatest senators, along with Henry Clay, Daniel Webster, John C. Calhoun, and Robert M. La Follette, Sr.[2]

On October 17, 1914, he married Martha Wheaton Bowers (1889–1958),[5] daughter of Lloyd Wheaton Bowers and Louisa Bennett Wilson. Taft himself appeared taciturn and coldly intellectual, characteristics that were offset by his gregarious wife, who served the same role his mother had for his father, as a confidante and powerful asset to her husband's political career. In 1949, Martha suffered a severe stroke which left her an invalid; after her stroke, Taft faithfully assisted his wife, even helping to feed and take care of her at public functions, a fact which, his admirers noted, belied his public image as a cold and uncaring person. They had four sons: William Howard Taft III (1915–1991), who became ambassador to Ireland; Robert Alphonso Taft Jr. (1917–1993), who was also elected to the U.S. Senate; Lloyd Bowers Taft (1923–1985),[6] who worked as an investment banker in Cincinnati,[7] and Horace Dwight Taft (1925–1983), who became a professor of physics and dean at Yale.[8] Two of Robert and Martha's grandsons are Robert Alphonso "Bob" Taft III (born 1942), Governor of Ohio from 1999 to 2007, and William Howard Taft IV (born 1945), Deputy Secretary of Defense from 1984 to 1989.

In 1917, Taft and his wife bought a 46-acre (190,000 m2) farm in Indian Hill, a well-to-do suburb of Cincinnati. Called Sky Farm, it would serve as Taft's primary residence for the rest of his life. The Tafts gradually made extensive renovations that turned the small farmhouse into a sixteen-room mansion. On the farm Taft enjoyed growing strawberries, asparagus, and potatoes for profit. During the summer, Taft often vacationed with his wife and children at the Taft family's summer home at Murray Bay, in Quebec, Canada.[9] Although he was nominally a member of the Episcopal church, his biographer James Patterson noted that Taft's "religious inclinations were weak" and that he was a "Sunday morning golfer, not a church-going Episcopalian."[10] When reporters asked his wife Martha what church he attended, she jokingly replied, "I'd have to say the Burning Tree", an exclusive country club and golf course in suburban Washington.[11]

When the United States entered World War I in April, 1917 Taft attempted to join the army but was rejected due to his poor eyesight. Instead, he joined the legal staff of the Food and Drug Administration where he met Herbert Hoover, who became his idol. In 1918 and 1919, he was in Paris as legal adviser for the American Relief Administration, Hoover's agency to distribute food to wartorn Europe. He came to distrust governmental bureaucracy as inefficient and detrimental to the rights of the individual, a principle he promoted throughout his career. He urged membership in the League of Nations[12] but generally distrusted European politicians. He endorsed the idea of a powerful world court to enforce international law, but no such idealized court ever existed during his lifetime. He returned to Cincinnati in late 1919, promoted Hoover for president in 1920, and opened a law firm with his brother, Charles Taft. In 1920 he was elected to the Ohio House of Representatives, where he served as Speaker of the House in 1926. In 1930, he was elected to the Ohio Senate, but was defeated for re-election in 1932; it would be the only general election defeat of his career. He was an outspoken opponent of the Ku Klux Klan, and he did not support prohibition. In 1925 he voted against a bill, sponsored by Ohio state representatives who were members of the Ku Klux Klan, to outlaw dancing on Sundays, and he led the fight against a Klan-sponsored bill requiring all Ohio public school teachers to read at least ten verses of the Bible each day in class.[13] In his speech opposing the bill, Taft stated that religion should be taught in churches, not public schools, and while the Bible was great literature, "in it religion overshadows all else." The bill passed the legislature over the opposition of Taft and his allies, but it was later vetoed by Ohio's governor.[13]

Taft's period of service in the Ohio state legislature was most notable for his efforts to reform and modernize the state's antiquated tax laws.[14]

Throughout the 1920s and 1930s, Taft was a powerful figure in local and state political and legal circles, and he was known as a loyal Republican who never threatened to bolt the party. He confessed in 1922 that "while I have no difficulty talking, I don't know how to do any of the eloquence business which makes for enthusiasm or applause."[15] A lackluster speaker who did not mix well or glad-hand supporters, Taft was still a tireless worker with a broad range of policy and political interests. His total grasp of the complex details of every issue impressed reporters and politicians. (Democrats joked, "Taft has the best mind in Washington, until he makes it up.")

Taft's loyalty to the conservative politicians who controlled Ohio's Republican Party had a price, as it often caused conflict with his younger brother, Charles, who as a local politician in Cincinnati had gained a reputation as a party maverick and liberal. However, despite their occasional policy disagreements, Charles loyally supported all three of his brother's presidential bids.

Taft was elected to the first of his three terms as US Senator in 1938 when he defeated the Democratic incumbent, Robert Bulkley. Taft engaged Bulkley in several debates and was generally regarded as the winner.[16] He struggled in the earlier debates but later came out on top through assistance from his wife, Martha,[16] who would be regarded as the most valuable asset in his campaign.[17] As a result, Taft gained the upper hand against Bulkley, who had earlier been regarded as the frontrunner in the race,[16] and won the election.

Co-operating with Conservative Democrats, he led the Conservative Coalition that opposed the New Deal. The Republican gains in the 1938 elections, combined with the creation of the Conservative Coalition, had stopped the expansion of the New Deal. However, Taft saw his mission as not only stopping the growth of the New Deal but also eliminating many of its government programs.

During his first term in the Senate, Taft criticized what he believed was the inefficiency and waste of many New Deal programs and of the need to let private enterprise and businesses restore the nation's economy instead of relying upon government programs to end the Great Depression. He condemned the New Deal as socialist and attacked deficit spending, high farm subsidies, governmental bureaucracy, the National Labor Relations Board, and nationalized health insurance. However, he did not always follow conservative ideology; for instance, after investigating the lack of adequate housing in the nation, he supported public housing programs.[18] He also supported federal aid to the states to fund public schools.[19]

Taft set forward a conservative domestic program that promoted limited government spending, a balanced federal budget, low taxes, pro-business policies to spur economic growth, a limited number of social welfare programs (such as Social Security, a minimum wage, public housing and federal aid to public education), and an adequate national defense focused on strengthening the Navy and Air Force.[20] In foreign policy, he advocated noninvolvement in European wars and military alliances.[21] He also strongly opposed the military draft on the principle that it limited a young man's freedom of choice.[22] Various historians have described Taft, in terms of political philosophy, as a libertarian; he opposed nearly all forms of governmental interference in both the national economy and in the private lives of citizens.[23]

Taft's greatest prominence during his first term came not from his fight against the New Deal but rather from his vigorous opposition to US involvement in the Second World War. A staunch non-interventionist, Taft believed that America should avoid any involvement in European or Asian wars and concentrate instead on solving its domestic problems. He believed that a strong military, combined with the natural geographic protection of the Atlantic and Pacific Oceans, would be adequate to protect America even if Germany overran all of Europe. Between the outbreak of war in September, 1939 and the Japanese attack on Pearl Harbor in December 1941 Taft opposed nearly all attempts to aid countries fighting Germany. That brought him strong criticism from many liberal Republicans, such as Wendell Willkie and Thomas E. Dewey, who felt that America could best protect itself by supporting the British and their allies. Although Taft fully supported the American war effort after Pearl Harbor, he continued to harbor a deep suspicion of American involvement in postwar military alliances, including North Atlantic Treaty Organization. Taft was the representative to speak in opposition to Japanese-American internment.[24]

In 1944 Taft was nearly defeated in his bid for a second term in the Senate. His Democratic opponent, William G. Pickrel, received major support from Ohio's labor unions and internationalists, and lost by fewer than 18,000 votes out of nearly three million cast, or a margin of less than one percent.[25] Taft lost Cleveland, the state's largest city, by 96,000 votes, and he trailed in most of Ohio's largest urban areas, but he carried 71 of the state's 88 counties and so avoided defeat.[25] Following his re-election, Taft became chairman of the Senate Republican Conference in 1944.

Taft condemned the postwar Nuremberg Trials as victor's justice under ex post facto laws, in which the people who won the war were the prosecutors, the judges, and the alleged victims, all at the same time. Taft condemned the trials as a violation of the most basic principles of American justice and internationally accepted standards in favor of a politicized version of justice in which court proceedings became an excuse for vengeance against the defeated.[26]

I question whether the hanging of those, who, however despicable, were the leaders of the German people, will ever discourage the making of aggressive war, for no one makes aggressive war unless he expects to win. About this whole judgment there is the spirit of vengeance, and vengeance is seldom justice. The hanging of the eleven men convicted will be a blot on the American record, which we shall long regret.[27]

His opposition to the trials was strongly criticized by Republicans and Democrats alike, and it is sometimes given as the main reason for his failure to secure the Republican nomination for president. Other observers, such as Senator John F. Kennedy (in Profiles in Courage), applauded Taft's principled stand even in the face of great bipartisan criticism.

When the Republicans took control of Congress in 1947, he focused on labor-management relations as Chair of the Senate Labor Committee. Decrying the effect of the Wagner Act in tilting the balance toward labor unions, he wrote the 1947 Taft–Hartley Act, which remains the basic labor law. It bans "unfair" union practices, outlaws closed shops, and authorizes the President to seek federal court injunctions to impose an 80-day cooling-off period if a strike threatened the national interest. Taft displayed all of his parliamentary skills in getting the bill through Congress. When President Harry Truman vetoed it, Taft then convinced both houses of Congress to override the veto.

From 1947 to 1949, when the Republicans controlled the Senate, Taft was his party's leading voice in domestic policy. He was reluctant to support farm subsidies, a position that hurt the party in rural areas (especially in the Midwest) in the 1948 elections. Taft engineered the passage of the Housing Act of 1949, which funded slum clearance and the construction of 810,000 units of low-income housing over a period of six years. It was one of the few Fair Deal proposals of Truman that he liked.[28]

In foreign policy, he was non-interventionist and did not see Stalin's Soviet Union as a major threat. However, he called David Lilienthal "soft on the subject of Communism."[29] The true danger, he believed, was big government and runaway spending. He supported the Truman Doctrine and reluctantly approved the Marshall Plan but opposed NATO, as unnecessary and provocative to the Soviets. He took the lead among Republicans in condemning Truman's handling of the Korean War and questioning the constitutionality of the war itself:: "My conclusion, therefore, is that in the case of Korea, where a war was already under way, we had no right to send troops to a nation, with whom we had no treaty, to defend it against attack by another nation, no matter how unprincipled that aggression might be, unless the whole matter was submitted to Congress and a declaration of war or some other direct authority obtained."[30]

Taft was a supporter of the new state of Israel, called for an end to the arms embargo to the Middle East, and supported arms shipments and other military aid to the new country.[31]

In 1950, Taft ran a more effective campaign for re-election to the Senate. Wooing factory workers, he visited 334 industrial plants and gave 873 speeches.[32] He won a third term by 431,184 votes, the second largest victory margin in Ohio Senate election history until then.[33] He benefited from a weak Democratic opponent – one observer reportedly said of "Jumping Joe" Ferguson, the State Auditor, "If the Democrats want to win, they should send Ferguson on a mission abroad," but more importantly, Ohio's unions failed to use the Taft-Hartley Act of 1947, which they denounced as a "slave labor law," against him. Additionally, Democratic Governor Frank Lausche did not endorse Ferguson and, according to journalist Sidney Lubell, almost openly supported Taft. In a post-election survey of voters, Lubell found that the overly aggressive, labor-backed anti-Taft campaign angered some Democrats.

Even many union members reportedly voted Republican to express their opposition to local union leaders, to support Taft-Hartley's ban on the closed shop, or to prevent, as one told Lubell, "the Socialists from taking over the Democratic party."[34]

By the start of his third Senate term, Taft had been given the nickname "Mr. Republican."[30] He was the chief congressional ideologue and spokesman for the conservatism of the Republican Party and the acknowledged national leader of its conservative faction.[35]

While outsiders thought Taft was the epitome of conservative Republicanism, inside the party, he was repeatedly criticized by hardliners alarmed by his sponsorship of New Deal-like programs, especially federal housing for the poor. The real estate lobby was especially fearful about public housing. Senator Kenneth S. Wherry discerned a "touch of socialism" in Taft, and his Ohio colleague, Senator John Bricker, speculated that perhaps the "socialists have gotten to Bob Taft." The distrust on the right hurt Taft's 1948 presidential ambitions.[36]

Taft first sought the Republican presidential nomination in 1940 but lost to Wendell Willkie. Taft was regarded as a strong contender, but his outspoken support of a non-interventionist foreign policy, and his opposition to the New Deal in domestic policy led many liberal Republicans to reject his candidacy. At the 1940 Republican Convention, Willkie, once a Democrat, and a corporate executive who had never run for political office, came from behind to beat Taft and several other candidates for the nomination. That year, Taft first clashed with Thomas E. Dewey, then a New York District Attorney, who had become nationally famous for successfully prosecuting several prominent organized-crime figures, especially New York mob boss "Lucky" Luciano. Taft felt that Dewey was not conservative or consistent enough in his principles for the Republican Party: "Tom Dewey has no real courage to stand up against the crowd that wants to smear any Republican who takes a forthright position against the New Deal... there is only one way to beat the New Deal, and that is head on. You can't outdeal them."[37] In other letters, Taft described Dewey as "very arrogant and bossy" and worried that "advisers will talk Dewey into too much internationalism...he comes from New York and sees the group opinions there as a lot more important than they are."[38]

In the 1944 presidential campaign Taft was not a candidate. He supported Governor John W. Bricker of Ohio, a fellow conservative, for the nomination. However, Bricker was defeated by Dewey, who had become the Governor of New York in 1943. Dewey named Bricker as his running mate; the ticket would go on to lose to Roosevelt in the general election.

In 1948, Taft made a second try for the nomination but again was defeated by his archrival, Dewey, who led the GOP's moderate/liberal wing. In the 1948 presidential election, Dewey was defeated by the Democratic presidential candidate, Harry S. Truman.

Taft sought to reach out to southern Democratic voters in his 1952 campaign. It was his third and final try for the nomination; it also proved to be his strongest effort. At the Republican State Convention in Little Rock, he declared:

I believe a Republican could carry a number of southern states if he conducts the right kind of campaign.... Whether we win or lose in the South, we cannot afford to ignore public opinion in the southern states, because it influences national public opinion, and that opinion finally decides the election.... It is said that southern Democrats will not vote for a Republican candidate. They have frequently done so. They did so in Little Rock last November [1951] when they elected Pratt Remmel mayor. I refuse to admit that if the issues are clearly presented, the southern voters will not vote on the basis of principle....[39]

Taft had the solid backing of the party's conservative wing. Former US Representative Howard Buffett of Nebraska (father of billionaire Warren Buffett) served as one of his campaign managers.[40] With Dewey no longer an active candidate, many political pundits regarded Taft as the frontrunner. However, the race changed when Dewey and other moderates were able to convince Dwight D. Eisenhower, the most popular general of World War II, to run for the nomination. Eisenhower ran because of his fear that Taft's non-interventionist views in foreign policy, especially his opposition to NATO, might benefit the Soviet Union in the Cold War.[41]

The fight between Taft and Eisenhower for the nomination was one of the closest and most bitter in American political history. When the Republican Convention opened in Chicago in July 1952, Taft and Eisenhower were neck-and-neck in delegate votes. On the convention's first day, Eisenhower's managers complained that Taft's forces had unfairly denied Eisenhower supporters delegate slots in several Southern states, including Texas, where the state chairman, Orville Bullington, was committed to Taft. The Eisenhower partisans proposed to remove pro-Taft delegates in these states and replace them with pro-Eisenhower delegates; they called their proposal "Fair Play." Although Taft angrily denied having stolen any delegate votes, the convention voted to support Fair Play 658 to 548, and the Texans voted 33–5 for Eisenhower as a result. In addition, several uncommitted state delegations, such as Michigan and Pennsylvania, agreed to support Eisenhower.

The addition of the uncommitted state delegations, combined with Taft's loss of many Southern delegates by the Fair Play proposal, decided the nomination in Eisenhower's favor. Despite his bitterness at his narrow defeat and his belief that he had been unfairly ambushed by the Eisenhower forces (including Dewey), Taft issued a brief statement after the convention conveying his congratulations and support to Eisenhower. Thereafter, however, he brooded in silence at his summer home in Quebec, complaining, "Every Republican candidate for President since 1936 has been nominated by the Chase National Bank."[42] As the weeks passed, Eisenhower's aides worried that Taft and his supporters would sit on their hands during the campaign and that as a result Eisenhower might lose the election. In September 1952, Taft finally agreed to meet with Eisenhower, at Morningside Heights in New York City. There, to gain Taft's support, Eisenhower promised that he would take no reprisals against Taft partisans, would cut federal spending, and would fight "creeping socialism in every domestic field." In fact, Eisenhower and Taft agreed on most domestic issues; their disagreements were primarily in foreign policy.

Eisenhower firmly believed in NATO and was committed to the US support of anticommunism in the Cold War.

Following Eisenhower's election and the Republican takeover of Congress, Taft served as Senate Majority Leader in 1953, and he strongly supported Eisenhower's domestic proposals. He worked hard to assist the inexperienced new officials of the administration. He even tried, with little success, to curb the excesses of red-baiting US Senator Joseph McCarthy. By April, Eisenhower and Taft were friends and golfing companions, and Taft was praising his former adversary. Defeat in 1952, it seemed, had softened Taft. No longer burdened by presidential ambitions, he had become less partisan, less abrasive, and more conciliatory; he was now widely regarded as the most powerful man in Congress.

On May 26, 1953, Taft delivered his final speech, in which he presciently warned of the dangers of America's emerging Cold War foreign policy, specifically against US military involvement in Southeast Asia, which would later become the Vietnam War:

“

I have never felt that we should send American soldiers to the Continent of Asia, which, of course, included China proper and Indo-China, simply because we are so outnumbered in fighting a land war on the Continent of Asia that it would bring about complete exhaustion even if we were able to win.... So today, as since 1947 in Europe and 1950 in Asia, we are really trying to arm the world against Communist Russia, or at least furnish all the assistance which can be of use to them in opposing Communism.

Is this policy of uniting the free world against Communism in time of peace going to be a practical long-term policy? I have always been a skeptic on the subject of the military practicability of NATO.... I have always felt that we should not attempt to fight Russia on the ground on the Continent of Europe any more than we should attempt to fight China on the Continent of Asia.[43]

In early 1953, Taft began to feel pain in his hips, and after a painful golf outing with President Eisenhower in April 1953 he entered Walter Reed Hospital for initial tests which led doctors to suspect a tumor or arthritis.[44] On May 26 he entered Holmes Hospital in Cincinnati for more extensive tests.[45] The doctors there discovered nodules on his forehead and abdomen, and after doing biopsies of samples of the nodules, found that they were malignant.[46] On June 7, he entered New York Hospital for more tests and treatment; to keep the news that he might have cancer a secret he registered under the assumed name "Howard Roberts, Jr.".[47] His doctors there agreed with the diagnosis of cancer, but disagreed as to the source of the primary tumor and method of treatment. Some of his doctors advocated exploratory surgery to keep the malignancy from spreading, while other doctors thought the tumors had spread too far, were inoperable, and recommended x-ray therapy to keep him comfortable.[48] After his death, an autopsy determined that Taft had been stricken with pancreatic cancer, which had quickly reached metastasis and spread throughout his body.[49] On June 10, 1953, Taft transferred his duties as Senate Majority Leader to Senator William F. Knowland of California. He did not resign his Senate seat and told reporters that he expected to recover and return to work.[50] However, his condition rapidly worsened, and Taft returned to New York Hospital for surgery on July 4 during a Senate recess. The surgery "did not take long, for the doctors quickly discovered cancer everywhere...there was no longer any doubt" that his condition was terminal.[51] He died at New York Hospital on July 31, following a final brain hemorrhage just hours after his wife's final visit.[49][52] His body lay in state in the Rotunda of the United States Capitol, where thousands of mourners offered their respects at his coffin.[53] On August 3, 1953, a memorial service was held in the rotunda; in addition to his family the service was attended by Eisenhower, Vice-President Nixon, the cabinet, members of the Supreme Court, and Taft's congressional colleagues. Following the service his body was flown to Cincinnati, where he was buried in a private ceremony at Indian Hill Episcopal Church Cemetery.[53]

In 1957, a committee led by Senator John F. Kennedy selected Taft as one of five great senators whose portraits would adorn the President's Room off the Senate floor. Kennedy would feature him in Profiles in Courage, and Taft continues to be regarded by historians as one of the most powerful senators of the 20th century.[54]

The Robert A. Taft Memorial, featuring a 10-foot (3.0 m) statue by the sculptor Wheeler Williams and a bell tower, is located north of the Capitol on Constitution Avenue. The inscription on the tower face behind him reads:

"This Memorial to Robert A. Taft, presented by the people to the Congress of the United States, stands as a tribute to the honesty, indomitable courage, and high principles of free government symbolized by his life."[55]